failed my emissions test- high nox - F-Body Road Racing and Autocross Forums

I failed my emission test yesterday on my 94 LT1 z28.

NOX was at 640 vs 480 limit. HC and CO were fine. According to what I have read, high NOX can be caused by high engine temps, EGR malfunction or too much timing. My engine run pretty cool (at about the 1/8 mark while cruising and at the 1/4 mark during stop and go in the summer) so I think I am ok there.

EGR System
Any ideas on how to test the egr system? I took it out after the test and sprayed it with some carb cleaner. It didnt appear to be *that* dirty. I tried pushing down on the plunger part and it moved up and down but there was a bit of resistance - should these things be really easy to move?

Timing
I have a mail order tune and it has the timing advanced... Do you think returning it to stock will be enough to get the NOX down 160 ppm NOX???

Any other suggestions would be greatly appreciated.

torontoZ28 View Member Profile	Sep 10 2007, 01:01 PM Post #1
Member Group: Advanced Members Posts: 195 Joined: 16-November 04 From: Toronto, Ontario, Canada Member No.: 543	I failed my emission test yesterday on my 94 LT1 z28. NOX was at 640 vs 480 limit. HC and CO were fine. According to what I have read, high NOX can be caused by high engine temps, EGR malfunction or too much timing. My engine run pretty cool (at about the 1/8 mark while cruising and at the 1/4 mark during stop and go in the summer) so I think I am ok there. EGR System Any ideas on how to test the egr system? I took it out after the test and sprayed it with some carb cleaner. It didnt appear to be that dirty. I tried pushing down on the plunger part and it moved up and down but there was a bit of resistance - should these things be really easy to move? Timing I have a mail order tune and it has the timing advanced... Do you think returning it to stock will be enough to get the NOX down 160 ppm NOX??? Any other suggestions would be greatly appreciated.